The present invention concerns a reinforced conductive layer, which is applied at a part of an electronic or electrical unit, e.g. a telephone, which is to come into contact with another part. The layer is mechanical, chemical and/or electrochemical resistant, The layer will protect the covered material against corrosion due to formation of a galvanic element.
In order to shield an electronic unit, preferably a telephone, against electromagnetic radiation such as ESD currents, it is at least partly surrounded by a conductive shield. This shield consists of a conductive material such as magnesium, aluminium, zinc or any other metal. It can also consist of a non-conductive material such as plastic, which is furnished with a conductive material, e.g. a conductive layer, which is able to conduct an electric current. The shield of the electronic unit will then be conductive to a desired extent.
In these contexts and for other reasons it is normal that different kinds of metals will come into contact with each other. This will lead to the creation of a galvanic element under influence of moisture or other fluids, whereby corrosion will result on at least one of the conductive materials. This will normally occur on the least noble metal. The different metals will come into contact when at least two parts of the electronic unit come into contact with each other. These parts may be placed at different parts of the electronic unit, e.g. at snaps, grooves, hooks, flanges, slots, screw joints, printed circuit carts or connectors.
For mobile telephones, one part of the shield forms the rear of the mobile telephone, which part is made of e.g. magnesium. Another part of the shield forms the front of the mobile telephone, which part may be of plastic, coated on the inside with a conductive layer mainly of silver, aluminium or the like. This layer may be coated by means of vacuum evaporating, spraying, painting, attaching a foil or may be a separately inserted conductive layer.
When the different materials come into contact with each other, a conductive unit will be formed as the shield parts are connected electrically. If this takes place in a damp environment, a galvanic element is formed. This will cause corrosion of the least noble metal, which will be decomposed and pulverised. This means that the contact between the two shield parts deteriorates, impairing or breaking the desired electrical connection between the shield parts. Furthermore, damage is created in the material. This damage is unaesthetic and also forms openings that will make the telephone loose, and lets in foreign particles such as sand, dirt, moisture and gases, which all harm the function of the telephone.
Sometimes a packing is placed between the shield parts to enhance the tightness and the contact ability between these parts. The packing is conductive and may be of steel or another metal or may be of a conductive, rubber like material. Hereby further materials that may form a galvanic element are introduced. Furthermore, there are a number of contact points where, as stated above, different metals come into contact with each other which leads to the above stated problems.
One object of the present invention is to reduce or eliminate the drawbacks of the above constructions. This is done by furnishing at least one of the parts that are to come into contact with each other with a protective conductive layer. The layer mechanically and electrically hinders/counteracts corrosion due to the formation of galvanic elements. The corrosion described above may of course arise anywhere in the electronic unit where two different metals come into contact with each other and where moisture is present and give rise to the above stated damages.
A reinforced conductive layer is provided, which layer is placed above one of the conductive materials which otherwise would have been susceptible to corrosion. The layer may be applied by tampon printing, screen printing, vacuum evaporation, painting, spraying or foiling. The layer may be applied in more than one layer. This protective layer can be made of any conductive metal. Most important is that the material has a mechanical and chemical resistance and that it will hinder moisture from reaching the underlying layer, which is to be protected, excluding any corrosion.
A preferred embodiment of the invention is provided if the protective layer is made of the same conductive material as the material it will come into contact with. In this way no galvanic element will be formed. Moisture or other chemical materials cannot go in under the reinforced conductive layer, and thus no corrosion will be formed. Accordingly the invention stops the harmful influences.
At e.g. the edges of a shield part of a mobile telephone, consisting of magnesium, the connecting parts are furnished with a conductive layer of a colour including silver, which layer is applied by e.g. tampon printing. The other shield part of the mobile telephone is made of a plastic, the inside of which is furnished with a conductive paint layer through tampon printing and which layer mainly consists of silver. As the magnesium will not come in direct contact with the silver, silver will meet silver and no galvanic element will be formed, The magnesium is protected by the silver paint, forming a reinforced conductive layer and moisture will not reach the magnesium.
The reinforced layer should be mechanically resistant and have an adhesiveness which is enough to guarantee that no holes will form in the layer and that the layer will not come off due to mechanical wear. Furthermore, the layer may be furnished with coarse metallic grains, in order to have better electrical contact between the connecting parts. The layer has a structure in which the metal grains are protected from mechanical influence and corrosion of a binder, preferably a plastic, e.g. acrylic, PVC, or a resin, whereby the metal grains will not be decomposed in any large extent. The thickness of the layer is normally 4 to 20 micrometers.
If a metal packing is placed between the shield parts, the reinforced conductive layer will still function, as the metal of the packing and the magnesium material will not come into contact with each other.